How would competition prevent ratings agencies from poorly aligned incentives? The "fitness function" of how good an agency is will be determined by the custom

How would competition prevent ratings agencies from poorly aligned incentives? The "fitness function" of how good an agency is will be determined by the customer, who only wants to receive the highest ratings. AFAIK, to rate a company/tranch/etc., the ratings agencies need access to internal company information. There's no room for an outsider ratings group to call bullshit -- people are only going to listen to the agency given internal info, the one hired by the company getting the rating. More competition wouldn't make the outside groups any more relevant, and without revenue, they would likely quickly dry up.